Assistive technologies are important for people with severe disabilities to lead a self-supportive, independent life. Persons severely disabled as a result of causes ranging from traumatic brain and spinal cord injuries to stroke generally find it extremely difficult to carry out everyday tasks without continuous assistance. Assistive technologies that help them communicate their intentions and effectively control their environment, especially to operate a computer, can greatly improve the quality of life for this group of people and may even help them to be employed.
Several assistive technology devices are presently available that are controlled by switches. For example, the switch integrated hand splint, blow-n-suck (sip-n-puff) device, chin control system, and electromyography (EMG) switch are all switch-based systems and can provide the user with some limited degrees of freedom. A group of head-mounted assistive devices has been developed that emulate a computer mouse with head movements. Cursor movements in these devices are controlled by tracking an infrared beam emitted or reflected from a transmitter or reflector attached to the user's glasses, cap, or headband (Chen et al. 1999; Takami et al., 1996). Tilt sensors and video-based computer interfaces that can track a facial feature have also been implemented (Chen, 2001; Betke et al., 2002). A limitation of these devices is that only those people whose head movement is not inhibited can avail of the technology. Another limitation is that the subject's head should always be in positions within the range of the device sensors. For example the controller may not be accessible when the subject is lying in bed or not sitting in front of a computer.
Another category of computer access systems used in assistive technologies operate by tracking eye movements from corneal reflections (Hutchinson et al., 1989) and pupil position. Electro-oculographic (EOG) potential measurements (Xie et al., 1995; Gips et al., 1993) have also been used for detecting eye movements. A limitation of these devices is that they affect the subject's eyesight by requiring extra eye movements that can interfere with the subject's normal visual activities such as reading, writing, and watching.
Some available assistive devices can provide proportional control. Most of these devices, however, require some degree of physical ability such as foot movement, hand or finger movements, or head movement. The needs of persons with severe motor disabilities such as those with amyotrophic lateral sclerosis (ALS) or middle to advanced locked-in syndrome, who cannot benefit from mechanical movements of any extremities can potentially be addressed by utilizing electric signals originated from brain waves or muscle twitches. Such brain computer interfaces (BMI), either invasive, or noninvasive have been the subjects of extensive research activities (Lal et al., 2005). For example, BRAINFINGERS™ (Brain Actuated Technologies, Inc., Dayton, Ohio, U.S.A.) is a non-invasive solution consisting of a headband with three electrodes that sense and respond to surface electrical signals generated from forehead muscles, eye movements, and brainwave activities. THINK-A-MOVE™ (Think-A-Move, Ltd., Beachwood, Ohio, U.S.A.) is another interface platform, which utilizes the capabilities of the ear as an output device. BRAINGATE™ (Cyberkinetics Neurotechnology Systems, Inc., Foxborough, Mass., U.S.A.), on the other hand, is an example of an invasive technology using intracortical electrodes to record brain signals from the motor cortex area. All of these technologies rely on signal processing and complex computational algorithms, which can results in delays or significant costs. These technologies can also be susceptible to external noise and interferences. In addition, the subjects may not want to go through a brain surgery for the sake of regaining partial control over their environment.
Very few assistive technologies presently available have made a successful transition outside research laboratories and are widely utilized by severely disabled individuals. Financial, technical, and psychophysical factors affect the acceptance rate of an assistive technology. Among factors beneficial for adopting an assistive technology are the ease of usage and convenience in control. Operating the assistive device should desirably be easy to learn and require minimum effort on the subject's part. The device is desirably small, unobtrusive, low cost, and non- or minimally invasive. Finally, a factor that is often overlooked, but important to a disabled subject, is that the device is desirably cosmetically acceptable. Therefore, there is presently an unmet need for assistive technologies for the disabled that provide some or even all of such features.